In a wireless system which uses a scattered wave as a direct carrier, the conventional technology which may be called direction division duplex (DDD) is known. In this technology, a transmitted wave and a received wave are treated equivalently as duplex, using the difference in the directivity of an outgoing electromagnetic wave from a base station and an incoming electromagnetic wave to the base station with the help of a circulator. This technology is described in “RFID-Handbook, 2nd Japanese edition”, written by Klaus Finkenzeller, translated by Software Engineering Laboratory, published by Nikkan kogyo Shimbun, Ltd. May, 2004, p. 45.